Fuel pumps are employed in a variety of engine systems. Common rail fuel injection systems for compression ignition (diesel) internal combustion engines provide excellent control of all aspects of engine operation and require a pump to act as a source of high pressure fuel. One known common rail fuel pump is of radial pump design and includes three pumping plungers arranged at equi-angularly spaced locations around an engine driven cam. Each plunger is mounted within a plunger bore provided in a pump head mounted to a main pump housing. As the cam is driven in use, the plungers are caused to reciprocate within their bores in a phased, cyclical manner. As the plungers reciprocate, each causes pressurisation of fuel within a pump chamber defined at one end of the associated plunger bore in the pump head. Fuel that is pressurised within the pump chambers is delivered to a common high pressure supply line and, from there, is supplied to a common rail or other accumulator volume, for delivery to the downstream injectors of the common rail fuel system.
Such a fuel pump has an inlet valve for admitting fuel under low pressure and an outlet valve for letting out the pressurised fuel. Both inlet and outlet valves are non-return valves (also known as check valves)—each have a valve member which is a moving element biased by a spring to close a valve aperture.
For the inlet valve, the valve member forms a plunger. One end of the plunger is biased to close the valve aperture. The biasing spring is fixed to the other end of the plunger, the spring extending around the plunger shaft to a seat in the pump body. A spring seat is formed at the second end of the plunger to retain the biasing spring in compression between the two seats. A variety of approaches have been used to fix this spring seat: clipping the spring seat around the plunger shaft; press fitting a spring seat on to the plunger shaft; and welding or screwing the spring seat to the plunger shaft.
For the outlet valve, the valve member is a ball biased to close the valve aperture by the biasing spring. The ball is located in one end of the biasing spring. A spring seat fixed to a body of the valve retains the other end of the biasing spring. The same variety of approaches are used to fix this spring seat as for the inlet valve: clipping the spring seat inside the bore of the valve body; press fitting a spring seat into the valve body; and welding or screwing the spring seat to the valve body.
An example of such an arrangement is shown in WO 2006/125690 A1. This document describes a high pressure pump with an outlet valve in which a spring retainer is inserted into the outlet bore of the pump body and fixed into it by press fitting.
It is an object of the present invention to provide a valve assembly suitable for use in a fuel pump and which avoids or overcomes the limitations of the aforementioned types of valve assembly.